1. Field of the Invention
This invention relates to an optical system provided with a forward observation optical system and an entire lateral circumference-observation optical system.
2. Description of the Related Art
Optical systems which are disclosed, for example, in Japanese Patent Kokai No. 2005-261557, Japanese Patent Kokai No. Hei 9-248276, and Japanese Patent Kokai No. Hei 11-137512 respectively have been conventionally proposed as this kind of optical system. These optical systems are formed in such a way that it is possible to switch to various observation fields of view.
The optical system disclosed in Japanese Patent Kokai No. 2005-261557 is used for an endoscope in which the direction of a field of view can be changed. As shown in FIG. 1A, a direct-looking observation optical system 52 for an observation in the direction along an axis O1 of an insertion section 51, and a side-looking observation optical system 53 for an observation in the direction perpendicular to the axis O1 of the insertion section 51 are arranged in the tip portion of the insertion section 51. In FIG. 1A, 52a denotes an objective optical system for the direct-looking observation optical system 52, 53a denotes an objective optical system for the side-looking observation optical system 53, and 53b denotes a mirror which deflects light from the objective optical system 52a in the direction parallel to the optical axis of the direct-looking observation optical system 52. Also, an image-forming optical system 54 and a CCD 55 are arranged on the optical path common to the direct-looking observation optical system 52 and the side-looking observation optical system 53. Further, a rotary shutter 56 is arranged between: the objective optical system 52a and the mirror 53b; and the image-forming optical system 54. As shown in FIG. 1B, a through hole 57 as a stop is provided for the rotary shutter 56.
And, the optical system is formed in such a way that it is possible to acquire either: a three-dimensional observation image of an portion P in front of the insertion section 51 in the direction along the axis O1; or observation images of an portion Pin front of the insertion section 51 in the direction along the axis O1 and of an portion P′ in the direction different from the direction of the portion P in front of the insertion section in the direction along the axis O1, by rotating the rotary shutter 56 arranged on the optical axes of the objective optical systems 52a and 53a to selectively form an image by light flux passing through the through hole 57 by the CCD 55.
Also, the optical system disclosed in Japanese Patent Kokai No. Hei 9-248276 is used for a rigid endoscope in which the direction of a field of view can be changed. As shown in FIG. 2A, the optical system is provided with: an objective optical system 61, a relay lens system 62, and an eyepiece optical system 63 on the rigid-endoscope-60 side; and an image-forming optical system 65 and an image pickup element 66 on the TV-camera-64 side. The objective optical system 61 is provided with a front lens group 61′ which consists of: two objective lenses 61a and 61b which are arranged at the nearest position to an object and face toward the direct-looking direction and toward the side-looking direction respectively; a first prism 61c which light beams from the two objective lenses enter through its planes which differ from each other, respectively; a second prism 61d which light beams from the first prism 61c enter through the identical plane of the second prism; and a pupil-separating stop 61e which makes a separation of pupils 61ea and 61eb according to the above-described directions of fields of view (the direct-looking and side-looking directions). A rear lens group 61″ is arranged in the rear of the front lens group 61′ and the rear lens group 61″ is used for focusing light beams from the pupils 61ea and 61eb to form the image of an object.
An image I1 from more than one direction of a field of view which is formed through the objective optical system 61, and the pupils 61ea and 61eb are propagated toward the eyepiece optical system 63 by the relay lens system 62. In FIG. 2B, P2 denotes more than one pupil which is propagated by the relay lens system 62 and corresponds to the direction of each of the fields of view. An image I2 is formed between the relay lens system 62 and the eyepiece optical system 63, and more than one pupil P3 which corresponds to the direction of each of the fields of view is acquired through the eyepiece optical system 63.
A pupil-selecting stop 67 as a means for selecting the direction of a field of view is arranged in the rear of the pupils P3. The pupil-selecting stop 67 is provided with an opening section 67a which transmits light of only either the pupil 61ea or 61eb. And, the pupil-selecting stop 67 is arranged with the direction of the opening section 67a optionally selected, and it is possible to acquire an observation image in the direction of a field of view of either the direct-looking or side-looking direction, by imaging a light beam transmitted by the opening section 67a by the image pickup element 66.
Also, the optical system disclosed in Japanese Patent Kokai No. Hei 11-137512 is used for an endoscope in which the direction of a field of view can be changed. As shown in FIGS. 3A and 3B, a tip rigid section 71 is provided with a direct-looking objective lens 72, a side-looking objective lens 73, a mirror 74, and a solid-state image pickup device 75. The mirror 74 is formed so as to be capable of rotating on a driving element 76 through the driving element 76. In FIG. 3B, 77 denotes a light-intercepting plate which shields from light the surface of the mirror 74 on the direct-looking-objective-lens-72 side.
And, by the mirror 74 rotated by the driving element 76 and switching to light from the direct-looking objective lens 72 or to light from the side-looking objective lens 73 to make the light enter the solid-state image pickup element 75, it is possible to acquire an observation image in the direction of a field of view of either direct-looking or side-looking direction.
Now, in an observation of the inside of a pipe-shaped object using an endoscope or the like, when an observation in the forward field of view is performed in insertion of an endoscope or the like into the inside of the pipe-shaped object and a portion which requires a detailed observation is found in the inner surface of the pipe-shaped object after the insertion, there is a necessity to a detailed observation over the entire circumference of the inner surface of the pipe-shaped object including the portion with respect to the lateral field of view.
Also, for example, in an examination of a stomach, an engine pipe, or the like, an optical system by which it is possible to simultaneously perform observations in the forward field of view and in the field of view of the entire lateral circumference is highly demanded because: in an observation of the side of a pipe, there is fear of mistaking an examination position if it is impossible to identify a position in the direction of the depth of the pipe; and, also, in an endoscope provided with an optical system by which it is possible to perform an observation only in either of the forward field of view or the field of view of the entire lateral circumference, as often as an observation is performed in a different field of view, the endoscope provided with the optical system by which it is possible to perform an observation in a desired observation field of view must be inserted into the inside of the pipe all over again, a physical burden to a subject becomes large, and the work by an examiner becomes complicated.
Also, conventional optical systems by which it is possible to perform a simultaneous observation in the forward field of view and in the field of view of the entire lateral circumference include, for example, optical systems which are disclosed in Japanese Patent Kokai No. 2002-341409, Japanese Patent Kouhyou No. 2002-523801, and Japanese Patent Kokai No. 2004-312593 respectively.
As shown in FIG. 4, the optical system disclosed in Japanese Patent Kokai No. 2002-341409 is provided with a rotationally symmetric convex mirror 81, a camera 82 arranged at a position at which the camera faces the convex mirror 81, a transparent tubular body 83 which joins the convex mirror 81 to the camera 82, and lenses 85 which are placed inside a through hole 84 formed in the central portion of the convex mirror 81 or are placed on the axial line of the through hole 84. In FIG. 4, 82a denotes an image-forming lens and 82b denotes an image pickup element. And, light from the forward field of view passes through the lenses 85 and passes through the image-forming lens 82a to form an image on the central region 86 of the imaging plane of the image pickup element 82b, while light from the field of view of the entire lateral circumference is reflected by the convex lens 81 and passes through the image-forming lens 82a to form an image on the surrounding region 87 of the imaging plane of the image pickup element 82c. By the light forming an image in the above-described manner, it is possible to simultaneously acquire observation images in the forward field of view and in the field of view of the entire lateral circumference.
As shown in FIG. 5, the optical system disclosed in Japanese Patent Kouhyou No. 2002-523801 is provided with: a rotationally symmetric lens block 91 which is provided with convex reflexive surfaces 91a which are formed so as to transmit light from the forward field of view and so as to reflect light from the field of view of the entire lateral circumference; a lens block 92; a lens system 93 which is arranged in the front of the lens block 91; a lens system 94 which is arranged in the rear of the lens block 92; and an image-capturing device 95. And, light from the forward field of view passes through the lens system 93, enters the inside of the lens block 91, and passes through the lens block 93 and the lens system 94 to form an image on the central region of the imaging plane of the image-capturing device 95, while light from the field of view of the entire lateral circumference is reflected by the convex reflexive surfaces 91a and passes through the lens blocks 91, 92, and the lens system 94 to form an image on the surrounding region of the imaging plane of the image-capturing device 95. By the light forming an image in the above-described manner, it is possible to simultaneously acquire observation images in the forward field of view and in the field of view of the entire lateral circumference.
As shown in FIG. 6, the optical system disclosed in Japanese Patent Kokai No. 2004-312593 is provided with: a rotationally-symmetric convex reflexive mirror 101 which is provided with an opening section 101a in its central portion; a rotationally-symmetric reflexive mirror 102 which is arranged so as to face the convex reflexive mirror 101 and is provided with an opening section 102a in its central portion; a lens 103 which is placed in the opening section 102a of the reflexive mirror 102; and an image pickup means 104 which performs imaging by receiving reflexive light which is reflected by the convex reflexive mirror 101 toward the reflexive mirror 102 and is thereafter reflected by the reflexive mirror 102 toward the opening section 101a of the convex reflexive mirror 101 and incident light which is transmitted by the lens 103 and goes in toward the opening section 101a of the convex reflexive mirror 101. Besides, in FIG. 6, 105 denotes a transparent cover and 106 denotes an image-displaying apparatus. And, light from the forward field of view is transmitted by the lens 103 and passes through the opening section 101a to form an image on the central region of the image pickup plane of the image pickup means 104, while light from the field of view of the entire lateral circumference is reflected by the reflexive mirror 102 toward the opening section 101a of the convex reflexive mirror 101 and passes through the opening section 101a to form an image on the central region of the image pickup plane of the image pickup means 104 after the light from the field of view of the entire lateral circumference is transmitted by the transparent cover 105 and is reflected by the convex reflexive mirror 101 toward the reflexive mirror 102. By the light forming an image in the above-described manner, it is possible to simultaneously acquire observation images in the forward field of view and in the field of view of the entire lateral circumference.
As described above, the optical systems which are disclosed in Japanese Patent Kokai No. 2002-341409, Japanese Patent Kouhyou No. 2002-523801, and Japanese Patent Kokai No. 2004-312593 respectively are provided with an optical system which guides light from the forward field of view to an image pickup means, and an optical system which guides light from the field of view of the entire lateral circumference to the image pickup means, and it is possible to simultaneously acquire observation images in the forward field of view and in the field of view of the entire lateral circumference.
Now, in the case of an observation in each of the forward field of view and the field of view of the entire lateral circumference, a small proportion of the image-forming region for an observation image in each of the fields of view in the image pickup region of the image pickup means makes it difficult to perform a detailed observation, so that it is desirable to make a proportion of the image-forming region for an observation image in each of the fields of view in the image pickup region of the image pickup means as large as possible.
Accordingly, in a detailed observation in the field of view of the entire lateral circumference, it is desirable: to make a proportion of the image-forming region for observation images in the forward field of view in the imaging region of the imaging means to such a degree that a position in the direction of the depth of a pipe can be identified; and to make the image-forming region for observation images in the field of view of the entire lateral circumference as large as possible. Also, on the other hand, in a detailed observation in the forward field of view, it is necessary that the image-forming region for an observation image in the forward field of view accounts for the whole image pickup region of the image pickup means.